Update to support gzip in same way as DropWizard (#38)

This adds a number of new configuration settings, with the leaf keys matching the ones used by DropWizard. The new configuration settings are documented in the README.

In particular, this adds support for decompressing gzip-encoded request bodies (by way of the BiDiGzipFilter). The default mime type handling has changed; instead of defaulting to only compressing a particular list of mime types, the new default behavior is to compress all non-gzip mime types (matching the default behavior of Jetty's GzipFilter).

The old list was:
"application/json", "application/xml", "text/html", "text/plain", "application/javascript",
"application/x-javascript", "text/javascript", "text/css", "text/xml", "image/svg+xml"
Okay that's a good argument. I was concerned changing the set of compressed types would affect some of our internal systems but it seems it shouldn't change anything for our use case.

Can you update this pull request then I can merge it? Thanks.